The present invention relates to a photosensitive member having a surface protective layer, and in more detail it relates to a photosensitive member in which a surface protective layer is formed on a photosensitive layer the surface of which is made irregular.
Recently a variety of photosensitive layers to be used in the photosensitive member for electrophotography, which are constituted of selenium and other inorganic photoconductive or organic photoconductive materials, have been proposed. In general, those photosensitive layers with low hardness tend to be worn out in repeated usage due to abrasion with transfer paper, cleaning materials, developer and others, and the member becomes readily spoiled.
It is proposed to solve this problem that a surface protective layer is formed on the surface of the photosensitive layer with insufficient hardness.
As such a surface protective layer, vacuum thin layers, for example, a plasma-polymerized layer formed of an adequate organic compound or a vapor deposition layer formed of a metal compound, and the like have been proposed (see, for example, Japanese Patent Laid-Open Publication Sho-60 32055).
A photosensitive member with such a surface protective layer is superior in durability to a corresponding member without a surface protective layer and has satisfactory layer strength in usage for a long time under ordinary temperature and humidity. Its moisture resistance, however, is not enough sufficient after used for a long time. Blurs and flows come to be seen in copied images during repeated usage under high humidity.
Organic photosensitive members prepared by a coating method have very smooth surface due to so-called leveling effect characteristic to the coating method. For example, in terms of the ten-point mean roughness (Rz) specified in JIS-B-0601, only about 0.05 .mu.m of the surface roughness is observed. Not only in the case of using a substrate with smooth surface for the preparation of a photosensitive member but also in the case of using a substrate with so rough a surface as 0.5 to 1 .mu.m, the formation of a photosensitive layer having about 20 .mu.m thickness on the substrate will ordinarily give a surface of the photosensitive layer with so low a roughness as described above.
However, the direct formation of a vacuum thin layer on such a so smooth photosensitive layer will cause such problems as rise of residual potential and occurrence of black thread-like noise in copied images when the photosensitive member is used in an actual copying process.
According to the knowledge of the present inventors, these problems are considered to derive from the presence of residual potential accumulated near the interface of the organic photosensitive layer and the vacuum thin layer.
The organic photosensitive layer and the vacuum thin layer are essentially different in nature in regard to constituted materials and processing.
The photocarrier coming through the organic photosensitive layer cannot enter into the vacuum thin layer since there are no triggers at the interface between the vacuum thin layer and the organic photosensitive layer, and is considered to be gradually accumulated in the vicinity of the interface to be observed as the rise of residual potential.
In a copying machine, mechanical pressure by developer, cleaning blade and others affect on the surface of the photosensitive member causing partial compression against the organic photosensitive layer via the vacuum thin layer to form minute irregular shapes on the interface in the direction of rotation of the member. Such minute irregularities serve as triggers and the photocarrier passes the vacuum thin layer through such spots to combine with the electrical charges on the utmost surface allowing no accumulation of residual potential. It is thought that black thread-like image noise are formed because of the difference between the residual potential in the minute irregular parts and that in the parts with no such irregularities.
The different nature of the organic photosensitive layer and the vacuum thin layer has not been explained clearly in physical terms so far as the present inventors are aware. It is noted by the way that such a phenomenon has also been observed in negatively chargeable photosensitive member when the ionization potentials of the organic photosensitive layer and of vacuum thin layer are nearly equal or when the ionization potential of the vacuum thin layer is rather lower.
The present invention has been completed in reference to these situations, and solves the above problem by forming a surface protective layer comprised of a vacuum thin layer on the photosensitive layer, after a roughing treatment of the surface of the photosensitive layer, instead of conventional direct formation of a surface protective layer on intact photosensitive layer with no roughing treatment.
Techniques of roughing surface of the photosensitive member are reported in Japanese Patent Laid-Open Publication Hei-2 139566, Sho-59 146057 and others, but the photosensitive member with roughened surface specified in the present invention is quite different from these ones in regard to the extent and the object of roughing as well as the purpose and effects of the invention.